1. Technical Field
This invention relates to a turbocharger housing for an internal combustion (IC) engine, and more particularly, to such a turbocharger housing formed of a fiber reinforced ceramic matrix composite (FRCMC) material and methods for making it.
2. Background Art
The power than can be developed by an internal combustion engine is dependent on the type of fuel used and how efficiently the fuel is burned. That, in turn, is dependent on the supply of air being provided to the cylinders being sufficient to cause as complete a combustion of the fuel as possible. By increasing the density of air to the cylinders of the engine the fuel can be burned efficiently, and as a result power is increased. The density of the air flow can be increased by using a turbocharger. A turbocharger is a device consisting of an engine exhaust operated turbine which drives a centrifugal compressor. The compressed air is mixed with fuel and provided to the cylinders during the intake stroke. Because the compressed air is more dense, it contains more oxygen and so facilitates a more complete combustion of the fuel.
FIG. 1 depicts a schematic of a turbocharged engine. The turbocharger is powered by the engine's exhaust gases being forced out of the engine by the exhaust stroke. Exhaust gases flow from the exhaust manifold 10, into the turbocharger turbine wheel 15 and out of the exhaust outlet 17. The turbocharger turbine wheel rotates the compressor wheel 14 via a shaft 11. Ambient air is drawn in the inlet 16 and is compressed by the compressor wheel 14. The compressed air is mixed with fuel and ultimately routed to the engine cylinder 13.
FIG. 2 provides a more detailed view of the turbocharger apparatus itself. Exhaust air is received from the exhaust gas inlet 28 and routed though an annular channel. The exhaust gas exits the channel and turns the turbine wheel 15 which turns the compressor wheel 14 via the shaft 11. Ambient air is sucked into the air inlet 16 and compressed by the compressor wheel 14. The compressed air is routed to the inlet manifold/cylinders (not shown) via the compressed air discharge outlet 22. A first turbocharger housing 32 covers the turbine wheel 24. Another turbocharger housing 36 covers the compressor wheel 20. Turbochargers operate not only under conditions of extreme heat but also under extreme variations in temperature. On the exhaust or input side of the turbocharger temperatures around 1500 degree F. are common. On the output side, the air compressed by the compressor is typically 300 degree F. Hence, the turbocharger housing must withstand high temperatures and high temperature variation, especially on the exhaust.
Heretofore, various kinds of turbocharger housings for internal combustion engines have been employed. For instance, in racing applications, turbocharger housings have been constructed of light metals, such as thin wall stainless steel, to reduce weight.
Alternately, in designing turbocharger housings for the commercial industry, improved turbocharger efficiency and reduced underhood temperatures are required. Heat should ideally be conserved in the exhaust gas to get more efficient use of the turbocharger itself. Additionally, catalytic converters require hot exhaust gases in order to have efficient catalytic converter operation. Standard turbocharger housings are generally made of cast iron. Cast iron absorbs heat and cools the exhaust gases robbing energy which can be used to turn the turbine and precluding efficient catalytic converter operation. Specifically, cast iron has a substantial heat capacitance so that when the car is started up much of the energy from the exhaust gas goes to heating up the huge cold cast iron mass. Hence, turbine efficiency decreases and the exhaust air going to the catalytic converter is cold, impairing catalytic converter performance. As a result, presently there are very few turbochargers used on American automobiles. Additionally, cast iron has a relatively high coefficient of thermal expansion, which must be taken into account when considering design tolerances.
To prevent the common turbocharger housing problems, car, motorcycle, truck, train, and other machinery applications could utilize a better turbocharger housing than is provided by current technology. Depending on the application, this improved turbocharge housing should be constructed of material that is light, long wearing, and which has a low thermal expansion and low heat capacity, so as to conserve heat in the exhaust gases. This ensures a longer life and improved performance over the present technology.
Wherefore, it is an object of this invention to provide a lightweight, but high strength turbocharger housing which is ductile and fracture resistant.
Wherefore, it is an object of the preset invention to provide an turbocharger housing which can be formed into complex shapes and sizes as desired.
It is still another object of this invention to provide a turbocharger housing that has improved insulation characteristics and lower thermal conductivity, to conserve heat in the exhaust gases and so enhance thermal efficiency and if applicable catalytic converter effectiveness.
Wherefore, it is another object of the present invention to provide a turbocharger housing which is capable of withstanding high temperatures and thermally-induced strains.